frontends (xmlui): added a user_action attribute: this attribute indicate if the data is a result of a user interaction or an event from the backend (in the later case, the frontend can choose to avoid interrupting the user). Internally (in XMLUI), "FROM_BACKEND" is added to XMLUI.flags if the UI result from a backend event.

Use this module to temporary store files that need to be integrated to other
projects such as Wokkel.

For example, the changeset that introduced this folder adds RSM (XEP-0059)
support to Wokkel. The files in sat.tmp.wokkel are imported over the initial
wokkel files from sat.plugins.__init__.py